The invention concerns generally the use of certain protocols and services for conveying certain types of information between the different nodes of a telecommunication network. Especially the invention concerns the transmission of multimedia-related information between a terminal of a cellular radio network and a node computer of a fixed packet-switched network.
Multimedia is generally understood as the synchronized presentation of audiovisual objects to a user. It is typical to multimedia-related information that it may contain elements of highly different nature, like text, still images, simple graphical elements, video and sound.
MMS or Multimedia Messaging Service is a proposed way for arranging the delivery of messages containing multimedia-related information from one telecommunication device to another. With xe2x80x9cmultimedia-relatedxe2x80x9d information we mean both the actual payload data that represents presentable objects and the control information that tells a presentation device how to handle the payload data. According to the proposals, MMS should be applicable for conveying such messages to and from the terminals of packet-switched cellular radio networks such as GPRS (General Packet Radio Service) and the packet-switched parts of UMTS (Universal Mobile Telecommunication System) in a store-and-forward manner much like the SMS (Short Messaging Service) text messages are conveyed in the second generation digital cellular networks, e.g. GSM (Global System for Mobile telecommunications).
FIG. 1 illustrates some system aspects of a known proposal for arranging the transmission of MMS messages between two mobile terminals 101 and 102. In FIG. 1 each terminal is operating in a cellular telephone system of its own: terminal 101 is a UMTS terminal operating in a UMTS network 103 and terminal 102 is an enhanced GSM terminal operating in an enhanced GSM network 104. From both networks there is a connection to a GPRS network 105. The UMTS network 103 comprises a UTRAN or UMTS Terrestrial Radio Access Network 106 as well as a CN or Core Network 107. In the enhanced GSM network 104 a BSS or Base Station Subsystem 108 and an MSC or a Mobile Switching Centre 109 are shown. The detailed structure of the network elements is unessential to the present invention, but it is known that for example a UTRAN consists of a number of Radio Network Subsystems, each of which in turn comprises a Radio Network Controller and a number of Node Bs roughly corresponding to base stations. A BSS in turn comprises a Base Station Controller and a number of Base Transceiver Stations operating under it. Various mixed-mode cellular telephone systems are possible; for example the BSS 108 might operate under the same CN as the UTRAN 106. The terminals could also be exactly similar terminals operating close to each other in a single cell.
In FIG. 1 there is a connection both from the UTRAN 106 and from the BSS 108 to a corresponding SGSN or Serving GPRS Support Node 110 and 111. Both of these are in turn coupled, through the GPRS trunk lines, to a GGSN or Gateway GPRS Support Node 112 which here also operates as an MMSC or a Multimedia Messaging Service Center. In analogy with the known SMS arrangements a terminal 101 may transmit an MMS message by identifying both the intended recipient""s terminal 102 and the MMSC through which the message is to be transmitted (actually the latter may even be left out if there is a default MMSC for each terminal). A Packet Control Unit or a corresponding functionality in the UTRAN 106 takes the MMS transmission and routes it through the current SGSN 110 to the MMSC 112 which stores the MMS message and commences the attempts for delivering it to the intended recipient. If there is an existing connection to the recipient""s terminal 102 the MMSC may deliver the message through the corresponding SGSN 111 and the BSS 108 to the terminal 102. If, however, the terminal 102 is temporarily shut off, out of coverage or otherwise unreachable, the MMSC retries the delivery at certain time intervals until either the message is successfully delivered or a timeout expires indicating that the message is obsolete and can be deleted undelivered. A positive or negative acknowledgement, depending on the success in delivery, may be returned to the transmitting terminal 101 if required.
At the time of filing this patent application there does not exist an unambiguously defined way of using the lower-level protocol layers and PDP Contexts (Packet Data Protocol) in the terminals and fixed network devices to convey the MMS messages. Somewhere at a relatively high level in the protocol stacks of both the terminals and the MMSC there must be an MMS-TP (Multimedia Messaging Servicexe2x80x94Transport Protocol) entity that uses the services offered by the lower level protocols to convey an MMS message first from the transmitting device to the MMSC and then further to the receiving device. Additionally the MMS messages must be mapped into PDP Contexts of certain type; the mapping will be closely related to the choice of lower protocol layers under the MMS-TP entity. We anticipate that network operators will require the MMS messaging to be distinguishable from other forms of packet-switched data transmission in order to arrange for a suitable charging scheme for the MMS services.
Two prior art solutions have been proposed for conveying MMS messages. One of them is to have a PDP Type separately defined for MMS, and to set up a PDP Context of that type between a terminal and an MMSC each time an MMS message has to be conveyed in either direction. This approach has the drawback of requiring a considerable amount of completely new specification and standardization work. Additionally new PDP Types are only very reluctantly accepted to the already frozen standards. The other proposed prior art approach is to build the MMS messaging on top of the known IP or Internet Protocol PDP Type. The latter approach would require the GGSNs to reserve and allocate dynamic IP addresses to mobile users. The use of dynamic addresses is not efficiently combined to MMS services, and in any case using the IP PDP Type for MMS messaging would consume the scarce IP addresses and involve the whole complexity of allocating and maintaining IP addresses and dynamically configuring hosts. A terminal roaming in another network should in practice always use the MMSC of its home network, because there is no possibility of dynamically telling the IP addresses of other MMSCs to the terminal.
It is an object of the present invention to provide a feasible method and a corresponding arrangement for conveying MMS messages between terminals and MMSCs. It is an additional object of the invention that the proposed method does not require exhaustive respecification in the framework of existing standards and proposals. A further object of the invention is to minimize the required protocol overhead in the MMS traffic between the terminals and the MMSCs. An even further object of the invention is to provide means for distinguishing the MMS traffic from other types of packet-switched information transfer.
The objects of the invention are met by using the OSP or Octet Stream Protocol, known as such, to carry a data stream comprising the required multimedia-related information.
The method according to the invention is characterized in that it comprises the steps of
defining a multimedia messaging transport protocol layer as a certain layer above an octet stream protocol layer in certain first and second protocol stacks and
exchanging multimedia-related information between the multimedia messaging transport protocol layer in a first device and the multimedia messaging transport protocol layer in a second device through the use of the octet stream protocol layer as well as other lower layers in the first and second protocol stacks.
The invention also applies to a terminal which is characterized in that its control block is arranged to
implement a multimedia messaging transport protocol layer in a protocol stack and
exchange multimedia-related information between said multimedia messaging transport protocol layer in the protocol stack and a network device through the use of an octet stream protocol layer as well as other lower layers in the protocol stack.
Additionally the invention applies to a network device which is characterized in that its control block is arranged to
implement a multimedia messaging transport protocol layer in a protocol stack and
exchange multimedia-related information between said multimedia messaging transport protocol layer in the protocol stack and a terminal through the use of an octet stream protocol layer as well as other lower layers in the protocol stack.
The Octet Stream Protocol or OSP is a previously defined way in GPRS for carrying relatively unstructured information in the form of octet streams between a mobile terminal and a GGSN. An octet is a group of eight consecutive bits. There exists a ready specified PDP Type for OSP, and in the known protocol stacks related to GPRS the OPS entity is directly on top of the SNDCP (Subnetwork Dependent Convergence Protocol) layer in the terminal and on top of the GTP (GPRS Tunneling Protocol) in the GGSN. According to the invention the MMS-TP protocol entity will be placed on top of the respective OSP entities in the terminal and the MMSC.
A PDP Context activation procedure between a terminal and a MMSC is required to enable the transmission of MMS messages in the framework of OSP. The device that initiates the activation procedure transmits an Activate PDP Context Request that contains a set of parameters that are required to identify and define the desired PDP Context. In the case of terminal-initiated PDP Context activation the SGSN may need to select the appropriate GGSN on the basis of the parameters contained within the activation request and possibly using also previously stored information about the home location of the terminal. If the MMSC functionality is not implemented within a GGSN, a specific interface may be needed to define the transmission of information therebetween.
After the PDP Context setup has been accomplished, MMS messages are conveyed as an octet stream by using either the octet mode, where the OSP protocol entity applies a packet assembly/disassembly function, or the block mode where no separate packet assembling or disassembling is performed.
The invention has several advantageous features. Using OSP as the bearer for MMS makes it possible to minimize protocol overheads because OSP does not require a large amount of associated control information. The PDP Context used to convey MMS messages may be completely separated from all other PDP Contexts even without defining a new PDP Type, which makes it easy to define a separate charging scheme for MMS. No IP addresses or other addresses of an external network are required for the transmission of MMS messages, which decreases configuration efforts, bypasses dynamic address allocation procedures and saves the operators from assigning static external network addresses to all users wishing to use MMS. Only the terminal and the MMSC or GGSN must interpret the data travelling through a xe2x80x9ctransparent tunnelxe2x80x9d between a terminal and a SGSN on one hand and between a SGSN and a GGSN on the other hand.
The utilization of an unstructured octet stream between a terminal and a MMSC or GGSN enables the operators to direct the MMS-carrying PDP Contexts of desired users always to a particular MMSC/GGSN; for example the one residing in the user""s home network. On the other hand, operators may also allow any MMSCs to be used, but this may restrict the service to the mobile-originated alternative only. In any case the control possibilities are much more flexible than in the IP-based prior art solutions. A terminal may even select a desired MMSC/GGSN by using a certain predefined parameter in an Activate PDP Context Request.